Accelerator for the vulcanization of caoutchouc substances



Patented Dec. 1%,, i923.

UNHTE WHOM W. BEDFORID, OF AKRON, OHIO,

ASSIGNOR' TO GOODYEAR, TIRE & RUBBEE COMPANY, OF AKRON, OHIO, ACORPORATIONOF OHIO.

accmnan'ron FOR THE VULCANIZATION F CAOUTCHOUC SUBSTANCEQ.

We brewing. original application filed January 6, 1917, Serial No.140,888. Divided and this application filed November 24, 1919. SerialNo. 340,261.

To all whom it may concern.

Be it known that I, CLAYTON W. Bnorono, a citizen of the United States,residin at Akron, in the county of Summit and tate 65 of Ohio, haveinvented new and useful Accelerators for the vulcanization of CaoutchoucSubstances, of which the following is a specification.

The present invention relates to the art of vulcanizing or curingcaoutchouc substances and more particularly to accelerators for usetherein, and will be fully understood from the following specification:

From the present knowledge of the art of curing rubber, either syntheticor natural,

it appears that the presence of nitrogen containing bodies duringvulcanization is essential to the formation of a practical or commercialproduct. Suitable nitrogen containing bodies may be found in naturalrubber, as obtained from latex, or may be added during the process ofmanufacture. The absence of nitrogen, however, results in a vulcanizedproduct having substantially no commercial value for many purposes. Ithas hence been the practice to add to the rubber mix, beforevulcanization, certain nitrogen containing bodies which improve theproperties of the product and shorten to the time required to cure it.

These nitrogen bodies have been known to the trade by the name ofaccelerators A large numberof publications may be found disclosing theuti ity and properties of certt tain specific nitro en bodies and ofcertain classes or types 0 nitrogen bodies as accelerators, these typesor classes having been classified according to their chemicalconstitution and reactions or by cerco tain physical properties such astheir dissociation constants, etc. All of these bodies will behereinafter included in the general term nitro en accelerators.

As set fort in my prior Patent No. 1,371,-

at 662,-granted March 15, 1921, of which this application is a division,I have found t at the nitrogen accelerators now known to the art are notusually the ultimate bodies which assist in the vulcanization of tocaoutchouc but that these ni-tro en accelerators must first re-act withsulp ur and that the sulphur re-action product thus formed is the agentwhich either aids or is entirely responsible for the satisfactoryvulcanization of the rubber with sulphur.

In the procedure heretofore utilized there are certain markeddisadvantages. For example, the temperatures used in vulcanizingcaoutchouc are only occasionally and by the merest coincidence thetemperatures most suitable for a reaction between sulphur and thenitrogen accelerator present. Thus, it is frequently the case that theproper temperature for vulcanization is not sufiiciently high to bringabout a satisfactory reaction between the nitrogen accelerator and thesulphur, which results in that a substance which is in reality a goodaccelerator appears to be wholly inactive, or does not exert its fullcuring power. For example, carbanilide is almost inactive at the usualvulcanization temperature corresponding to pounds of steam pressure,whereas at 60 to 80 pounds pressure it shows very valuable qualities.

In other cases nitrogen accelerators which.

possess, in fact, valuable properties, are regarded as commerciallyimpractical by reason of the fact that large volumes of gas are producedduring their reaction in the vulcanization process, the resultingproduct being correspondingly porous and defective. Since the gasesproduced during this reaction frequently contain ms and other malodorouscompounds, the product obtained is frequently very foul smelling. Thisis the case, for example, with such compounds as hexamethylenetetramineand urea, in the use of both of which large volumes of gas are liberatedduring the vulcanization process as a result of the reaction of thesebodies with sulphur.

In accordance with the present invention, the disadvantages abovedescribed have been avoided, the use of nitrogen accelerators invulcanization facilitated and the results of their use greatly improvedby first causing a reaction of the nitrogen accelerator with sulphur insuitable proportions prior to incorporation into the mix to bevulcanized. It is then possible to carry out the reaction between thenitrogen accelerator and the sulphur at the temperature best suitedthereto, and to remove any undesired gaseous or other by-products whichare formed as a result of the reaction with the nitrogen accelerator. Itis-therefore possible, by the present process, to employ many nitrogenaccelerquickly;

ators which at present are regarded as impractical or of no commercialvalue and to secure more advantageous results with many accelerators nowin use.

The first stage of my procem wherein the nitrogen accelerator is actedupon by sulphur prior to introduction into the other mix, may result ina substitution of sulphur in the nitrogen accelerator, indicated by theliberation of hydrogen sulphide and other volatile sulphur compounds,although sulphur addition and polymerization may, and probably do,occur.

- The proportions of a sulphur reactlon product of a nitrogenaccelerator, which will hereinafter be designated as asulphurnitrogenaccelerator, which are incorporated into the rubber mix, may be varied.Thus,-

in a mixture containing one part of sulphur, sixteen parts of zinc oxideand sixteen parts of pale-crepe plantation rubber, from onehalf part totwo parts of the sulphur nitrogen accelerator may be used. Such amixture may be vulcanized by heating under from forty to fifty pounds ofsteam pressure for from twenty to fifty minutes, the time required forcuring the rubber being greatly diminished by the addition of a, sulphurnitrogen accelerator. The resulting vulcanized product is of higherquality than alike mix, which is vulcanized without the accelerator, asevidenced by its higher tensile stren h, higher modulas of elasticityand etc. -urthermore, by shortening the time of cure, the output of agiven uipment is increased.

My preferred method for producing asulphur-nitrogen accelerator fromthiocarbanilide, for example, is as follows, the following ingredientsbeing used:

910 parts thiocarbanilide.

514 parts sul hur.

744 parts ani ine. The mixture is brought to a boil under an eificientreflux condenser, and the temperature of the'liquid gradually raised to190 C. This temperature is held until 133 arts (by weight) of gas havepassed throug the condenser. The liquid is now distilled with as littlerefluxing as is possible until 87 parts of aniline have been removed.If, at this point, the total gas loss has not reached 190 to 200 parts,a reflux condenser is again applied to the still and distillation withrefluxin continued until the gas loss reaches the gure given. Thetemperature at the end of the distillation of the aniline or at the endof the final reflux, ing rocess when the latter is used should reacbutnot exceed 270 C. The reaction is now complete and the reactionproduct suitable for use in the rubber mix.

In the. reaction above described it is obgen accelerator, which willform a substantial portion of the final product of the reaction.

As a further example of the process the following may be mentioned: 108parts paraphenylenediamine are mixed with 32 parts of sulphur. Themixture is melted together, being constantly stirred, and brought to atemperature of 180 to 200 0., care being exercised to prevent localover-heatm sided and the evolution of gas has dropped to a minimum, thereaction product is cooled, ground and sifted. This material which is anorganic compound, containin both sulphur and nitrogen, shows many avantageous properties as an accelerator over the original nitrogen body.

According to my invention, therefore, an entirely new class of nitrogencompounds is made use of for the purpose of bringing about thevulcanization of caoutchouc, these compounds being the reaction productsof sulphur with nitrogen accelerators, such reaction products beingobtained inde pendently of the vulcanization process both as re ardstime and lace tem erature ro-.

g P 7 a p portions -of ingredients or reactive substances, and all otherconditions. This new class of accelerators I identify ,by the termsulphur-nitrogen accelerators, that is, reaction products of elementalsulphur and nitrogen-containing bodies of the class or classes known asaccelerators. By the term nitrogen accelerators as employed herein, Iwish it to be understood, however, that I intend to define all of thosenitrogen containing bodies, the roperties of which are such that theyten to enter into reaction with sulphur in a rubber mix as the result ofwhich vulcanization of the mix is effected or expedited. As I havepointed out, many substances are inherently accelerators with inthis-broad sense, which would not be so regarded in the present state ofthe art, for

After the vigorous reaction has sub-- ncraaoa chemically and physicallyfrom the original. accelerator.

In addition to the amino bodies, secondary amines and imines, such asthe specific nitrogen accelerators heretofore mentioned, I find thatnitroso bodies, such as paranitrosodimethylaniline, cyanide bodies, suchas sodium ferrocyanidc, and proteids and the products of theirdecomposition and hydrolysis, including the amido acids, and such, forinstance, as animal glue or gelatine, give advantageous results whenemployed according to my process. It will be evident that in preparingthe sulphur-nitrogen accelerator of my invention, it is not necessary tolimit the amount of sulphur to that required for reaction with thenitrogen-accelerator. Although this is in some respects advantageous, itis permissible to admix the entire amount of sulphur to be used forvulcanization with the nitrogen accelerator.

While I have described in considerable detail the theories whichunderlie my present invention and have given certain specific examplesof procedure and materials to be employed, it will be understood that Ido notregard the-invention as dependent upon the soundness or accuracyofsuch theories, nor as limited to the specific procedure or materialsmentioned, except in so far as suchlimitations are included within theterms of the accompanyin claims, in which it is my intention to claimall novelty inherent in my invention as broadly as is permissible inview of the prior art.

What I claim as new and desire to secure by Letters Patent is:

1. The non-gaseous reaction product of a nitrogen accelerator andsulphur.

2. The sulphur addition product of a nitro en accelerator.

3. he non-gaseous reaction product of a nitrogen accelerator andsulphur, said product being freed from inert and deleterious materials.

4. The process of producing a sulphur .under reacting conditions.

7. The process of producing a sulphur nitrogen accelerator whichconsists in bringing together under reacting conditions in the presenceof an aromatic amine, thiocarbanilide and sulphur.

8. The process of producing a sulphur nitrogen accelerator which consistin bringing together thiocarbanilide, sulphur, and aniline, heating themixture to reduce re action 'therebetween, and removing the ex cess ofaniline.

9. The sulphur nitrogen accelerator com prising the reaction product ofsulphur upon thiocarbanilide in the presence of aniline.

CLAYTON W. nnnro nn.

